Hydrogen sulfide and ammonia recovery by degassing and plural distillation with ammonia recycle



June 30, 1970 R. J. KLETT 3,518,166

HYDROGEN SULFIDE AND AMMONIA RECOVERY BY DEGASSING AND PLURALDISTILLATION WITH AMMONIA RECYCLE Filed Sept. 26, 1968 HIGH .3 PRESSURENH3 DEGASSER 22 24\ lo a Hg$ 23 LOW 15 7 PRESSURE 2/ DEGASSER 20 Z5 12 ml 71 35 w 27 l3 0. g

(I II la 0) FEED SURGE E" TANK i z INVENTOR ROBERT J. KLETT ATTORNEYSUnited States Patent US. Cl. 203-78 6 Claims ABSTRACT OF THE DISCLOSUREOperation of a process to recover H 8 and NH from an aqueous solution ofH 8, NH and light hydrocarbons under superatmospheric pressure, whereinthe H 8 and NH are recovered separately from an H 8 Stripper and an NHstripper, respectively, is improved from a control and stabilitystandpoint, and aqueous feed solutions of high H S content are moreadvantageously handled by (l) combining an NH -rich, H S-lean condensatestream generated in the overhead system of the NH stripper with theaqueous solution of NH H 5, and light hydrocarbons; then (2) removinglight hydrocarbons as gases by reducing the pressure on the combinedsolution; (3) providing residence time for the combined solution; andthen (4) feeding the combined aqueous feed stream to the H 8 stripper.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to methods for recovering H 8 and NH from aqueous streamscontaining the same. More particularly, this invention relates toprocesses for separately recovering H 8 and NH from aqueous streams.

Description of the prior art containing nitrogen compounds and sulfurcompounds and recycle hydrogen-rich gas and makeup hydrogen are passedthrough a reaction zone, usually containing a catalyst, at elevatedtemperature and pressure at which at least a portion of the hydrocarbonsare vaporized; and

there is obtained as a reaction zone effluent a mixture of vaporizedhydrocarbons, hydrogen, H 5 and NH:. The efiluent may also containheavier hydrocarbons which are liquid at the reaction conditions. Thereaction effluent is cooled to condense vaporized hydrocarbons, wherebythe liquid hydrocarbons can be separated from hydrogenrich recycle gas,which is then reused in the process.

When the reaction effiuent contains both H 8 and NH it has been foundthat on cooling to temperatures below about 300 F. the H 8 and NH mayreact to form salts which sometimes cause clogging problems in the heatexchangers and the lines. Injection of water into the reaction efiiuentupstream of the heat exchangers has been used to wash out such depositsand/or to prevent their forming. This water injection can provide ameans of removing much of the NH formed, if rather large amounts ofwater are injected sufficient to dissolve the NH 3,518,166 Patented June30, 1970 In a typical hydroconversion process, such as hydrotreating orhydrocracking, there are considerable amounts of light hydrocarbons andhydrogen present in the reactron efiiuent. Upon washing H S and NH outof the rethe Water phase, particularly if the Washing is at a highpressure. In many hydroconversion processes, the Washing is done at apressure of 500 to 5,000 p.s.i.g., more well as a small portion of thehydrogen, will dissolve in action efiluent, a portion of these lighthydrocarbons, as typically 1,000 to 3,000 p.s.i.g. For example, inhydrotreating gas oil, the effiuent from the hydrotreater typically iscooled by heat exchange to a temperature between about and F. at apressure of 2,000 p.s.i.g. Be cause the water is mixed with the gaseouseffluent from the hydrotreater reactor at high pressure and before theeffluent is cooled to 100 to 150 F., significant amounts of lighthydrocarbons, such as methane, ethane, propane, butane, etc., willdissolve in the water.

These light hydrocarbons, as Well as dissolved hydrogen, may be removedfrom the aqueous phase prior to treatment to remove H 8 and NH, byreducing the pressure on the aqueous solution. It is desirable to retainH 8 in the aqueous solution when the pressure is reduced because (1) theH 8 is an impurity in the light hydrocarbon vapors; and (2) the H 8 ispreferably recovered in a single concentrated stream as a valuablebyproduct in a subsequent H 8 and NH recovery process. However, in manyinstances, the content of H 3 in the aqueous solution which isformede.g., in the overhead system of strippers or fractionatorsassociated with hydroconversion processes-is too high for the H 5 to besubstantially completely retained in the solution when the pressure isreduced.

Another problem that exists according to previous methods to recover H 8and NH separately from foul Water containing the same resides largely inobtaining steady and stable control of the strippers used to recover H 5and NH respectively. In the process described in US. Pat. 3,335,071issued to W. M. Bollen et a1. and assigned to Chevron Research Company,an aqueous solution of H 8 and NH may be treated according to thefollowing steps:

(a) Stripping the NH H 8 aqueous solution in a first strippingdistillation column to obtain as an overhead an H S-rich vapor and asbottoms an NH -rich aqueous bottoms solution;

(b) Stripping the NH -rich aqueous bottoms in a second distillationcolumn to obtain an NH -rich vapor overhead;

(c) Partially condensing the NH' -rich vapor overhead to obtain an NHrich vapor and an NHgI'lCh aqueous overhead condensate; and

(d) Recycling a portion of the NH -rich aqueuous overhead condensate tothe first distillation column (the H 8 stripper).

The disclosure of US. Pat. 3,335,071 is incorporated by reference intothe present specification.

Recycling the Nl-l -rich overhead condensate to the H S stripper ishighly desirable for some purposes, but fluctuations in the NH contentin this stream tend to cause periodic upsets in the H 8 stripperoperation. This is thought to be partly due to the considerable amountsof NH contained in the recycle relative to the amount of NH in the feedto the H 8 stripper. Although it is not completely understood why, insome instances when the NH content of the NH stripper overheadcondensate increases, a large bubble of NH would travel up the H 8stripper reducing the purity of the H 8 overhead and requiringadjustment in the overhead control in the H 8 stripper. Also, increasesin NH content of the recycle NH stripper overhead condensate result inhigher pres- 3 sures being required at the bottom of the H 8 stripperwhen operating at a given temperature. Because these changes would occurrelatively rapidly, steady and stable control of the H 8 stripper and NHstripper was not always attainable.

In summary, according to practices employed under the prior art,considerable amounts of H S may be lost from the aqueous solutiondesired to be treated for separate recovery of H 8 and NH when thepressure is reduced on the aqueous solution so as to remove lighthydrocarbons and/or hydrogen dissolved in the aqueous solution of H 8and NH Also, according to previously employed methods for separatelyrecovering H 5 and NH difficulties are incurred in attempting to obtainsteady and stable operation of the H 5 and NH strippers. In the processof the present invention, these problems are substantially overcome.

SUMMARY OF THE INVENTION According to the present invention, in aprocess for separately recovering H 8 and NH from a first aqueoussolution comprised of H 8, NH and light hydrocarbons undersuperatmospheric pressure according to the steps:

(a) Degassing the first aqueous solution by reducing the pressure,thereby removing light hydrocarbons and obtaining a second aqueoussolution comprised of H 8 and 3;

(b) Stripping H S out of the second aqueous solution in a firstdistillation column to obtain an H S-rich overhead stream and an aqueousbottoms stream of reduced H 8 content;

(c) Stripping NH out of the aqueous bottoms stream in a seconddistillation column to obtain an NH -rich vapor overhead; and

(d) Partially condensing the NH -rich vapor overhead to obtain an NH-rich vapor and an NH -rich overhead condensate.

The improvement is made which comprises:

(e) Combining at least a portion of the NH -rich overhead condensatewith the first aqueous solution to obtain a combined aqueous solution;then (f) Removing at least a portion of the hydrocarbons contained inthe first aqueous solution in a degassing zone as vapors by reducing thepressure on the combined aqueous solution to obtain said second aqueoussolution, and then (g) Passing the second aqueous solution to the firstdistillation column.

Operating in this manner avoids direct recycle of the NI-I stripperoverhead condensate to the H28 stripper; and improved control andstability of the H 5 stripper is obtained. In addition, the recycle ofthe NH -rich overhead condensate from the NH stripper to the degassingzone serves to retain H 8 in the aqueous phase while degassing lighthydrocarbons and/or hydrogen from the aqueous feed containing the H S-NHThe improved stability of the H 8 stripper is thought to be largely aresult of avoiding direct recycle of NH rich condensate. According tothe present invention, the NH -rich condensate is recycled to thedegassing zone where it achieves or closely approaches equilibrium withthe net feed to the H 8 stripper; and fluctuations in the feedcomposition are dampened out due to the extra residence time. Aresidence time of at least five minutes after combining the aqueousstreams and prior to introduction to the H 5 stripper is desirable. Muchmore preferable, a residence time of about one to three hours isprovided for the combined gross feed streams of recycle NH -richcondensate from the NH stripper and net H 8- NH aqueous feed solution.Still more preferable, a residence time of between about 3 and 24 hoursor longer is provided for the combined, that is gross, feed streams.Provision for residence time for the recycle NH -rich condensate priorto introduction to the H 8 stripper is in contrast to previous operationwherein the recycle of NH -rich condensate directly interconnected theH28 stripper and the NH, stripper so that upsets in either of thesestrippers could often affect the other stripper.

Also, it has been found that, if a residence time of about 24 hours orlonger is used, then oil may be essentially completely separated fromthe foul water feed streams so that the strippers are kept cleaner.Additionally, when the feed streams include foul water from fluidcatalytic cracking units or the like, the residence time of about 24hours or longer will allow hydrocyanide acids which are likely to bepresent in such foul water streams to be converted to thiocyanate.Conversion of the hydrocyanide to thiocyanate helps minimize corrosionproblems in the strippers.

It has been found that with the recycle of the NH overhead condensatelarge amounts of H 8 in the aqueous feed streams to the present processmay be dealt with without excessive losses of H S in the lighthydrocarbons and/ or hydrogen from the degassing step. Under mostconditions, the H 8 content of the gases from the degassing step is verylow. The degasser off-gases may be used as refinery fuel gas as only avery small amount of S0 will be produced by burning the gases. Thus airpollution is substantially reduced.

A number of streams containing H 8 and/ or NH;; may be treated in theprocess of the present invention, but it is preferable that there be avessel or some means to provide residence time and allow mixing of theNH rich condensate and the net feed to the present process. For example,there may be provided simply a surge vessel with no removal of lighthydrocarbons or a degasser to remove light hydrocarbons from at leastone of the feed streams to the present process. In the more usual case,it is necessary to provide a degassing step which in many instancesresults in loss of H 8 and/or extra expense to remove H S from the lighthydrocarbons when not using the process of the present invention. Asindicated above, the H 8 contents of the net feed streams may berelatively high in the present process but still dealt with withoutlarge H 8 losses or H 8 impurities in the degasser Zone off-gases. Therecycle of the NH stripper overhead condensate to the degasser zoneserves to retain H 8 in the aqueous phase.

In the process of the present invention, it has been found that it isadvantageous to use two stages of degassing. Use of two stages ofdegassing serves to further minimize the H 8 losses in the lighthydrocarbon streams which are removed from the aqueous solution when thepressure is reduced on the aqueous solution in the degassing zone. Thefirst stage of degassing is a high pressure degassing stage wherein thepressure is maintained between 50 and 500 p.s.i.g. Preferably thepressure is maintained at about 70 to 200 p.s.i.g. The liquid phaseaqueous solution from the high pressure degassing stage is then passedto a low pressure degassing stage.

Aqueous streams containing H 5 and/or NH together with small amounts oflight hydrocarbons, which light hydrocarbons are dissolved in theaqueous solution due to relatively low pressures, for example, 10p.s.i.g. to p.s.i.g., are advantageously introduced to the process ofthe present invention by combining such streams with the aqueoussolution fed to the low pressure degasser. The low pressure degasser ismaintained at a pressure between 0 p.s.i.g. and 50 p.s.i.g., preferablybetween 1 p.s.i.g. and 10 p.s.i.g

BRIEF DESCRIPTION OF THE DRAWING The drawing schematically illustrates apreferred embodiment of the present process for separately recovering HS and NH wherein two degassing stages are used.

DETAILED DESCRIPTION OF THE DRAWING AND THE INVENTION Referring now inmore detail to the drawing, an aqueous feed stream containing H S and NHis introduced to the process via line 1. In a preferred embodiment ofthe present invention, this aqueous feed stream is obtained bycommingling or contacting the efliuent from a hydrocracking reactor at apressure of about 2,000 p.s.i.g. with water. As indicated in thediscussion under Background of the Invention, this contacting is carriedout to remove ammonia and H S from the hydrocracker reactor efiluent.Because the hydrocracker reactor eifluent contains substantial amountsof hydrogen and light hydrocarbons, the aqueous solution which is formedis comprised of hydrogen and light hydrocarbons in addition to H S andNH In the process of the present invention, this aqueous solution iscombined with the recycle NH -rich aqueous stream obtained from theoverhead of the NH stripper, as will be described in more detailhereinbelow. The NH -rich aqueous solution is recycled via line 26.

A stream rich in H S obtained from the overhead of one of the strippingdistillation columns used to remove light hydrocarbons from thehydrocracker eflluent product is introduced to the process via line 2.Among the many H S-rich streams that may be treated in the process ofthe present invention are those streams derived from steam strippingliquid hydrocarbon etiluents from hydrotreating or hydrofiningprocesses. These liquid hydrocarbon eflluents contain H 8 and lighthydrocarbons which are removed by stripping or distillation. Thestripper or distillation column overhead vapors which result from thestripping operation contain appreciable amounts of H 8 which dissolve toa significant extent in the water formed when the overhead is partiallycondensed. Frequently the stripping is carried out at low pressures, forexample, 5 to 50 p.s.i.g., in the overhead accumulator. In thisinstance, these overhead condensate streams may be introduced to theprocess of the present invention via line 7. It is particularlyimportant to remove light hydrocarbons from the overhead condensatestreams when the H 8, which is removed from the H 8 stripper via line15, is desired in a highly purified form. For example, when the H 8 isto be used as feed to a Claus process for manufacture of sulfur, it isdesirable that the H 8 stream contain less than 0.1 volume percenthydrocarbons.

In some instances, the hydrocarbon effluent from the hydrotreating orhydrocracking process will be stripped or fractionated to remove H 8 andlight hydrocarbons at a pressure above 50 p.s.i.g. For example, in US.Pat. 3,356,608, a process is described wherein gas oil and hydrogen arecontacted with a sulfactive hydrogenation catalyst and the eflluenthydrocarbon stream, after separation of recycle hydrogen, is steamstripped at pressures above 150 p.s.i.g. Upon condensing the overheadfrom the stripper, an aqueous phase is formed which may be very rich inH S compared to aqueous solutions formed in the presence of H 8 at lowerH 8 partial pressures.

Referring again to the drawing, the combined streams 1, 2 and 26 areintroduced via line 3 to the high pressure degasser 4. In order toachieve low H 8 contents in the off-gases, the high pressure degasser ispreferably maintained at a pressure of about 185 p.s.i.g. and atemperature of about 80 F. Lower pressures and higher temperatures willresult in increased H 8 contents in the off-gas. Light hydrocarbons andhydrogen are removed via line 5 from the top of the high pressuredegassing vessel. When operating at about 100 to 200 p.s.i.g. and 80 to100 F., the H 8 content of stream 5 is generally less than 3 volumepercent. When operating at high pressure and low temperature for thehigh pressure degasser in accordance with the present invention, the H 8content may be maintained between about 0.1 to 2.0 volume percent. Thusstream 5 has a very low H 8 content and is generally suitable asrefinery fuel gas. The partially degassed aqueous solution is withdrawnfrom the bottom of the high pressure degasser via line 6.

An aqueous solution of H 8, NH and small amounts of dissolvedhydrocarbons, which aqueous solution is obtained as overhead condensatefrom a hydrocarbon stripper operating at an overhead pressure of about50 p.s.i.g., is introduced via line 7. The combined aqueous streams inlines 6 and 7 are passed via line 8 to low pressure degasser 9. The lowpressure degasser is preferably maintained at a pressure of about 2p.s.i.g. Light hydrocarbons are withdrawn in line 10 from the lowpressure degasser, and an aqueous solution of H 8 and NH is withdrawnfrom the bottom of the degasser via line '11. The H 8 content of stream10 is generally less than about 4 volume percent when operating inaccordance with the present invention. The percent of H 8 in the lowpressure degasser off-gases may be reduced further, for example, to therange for the high pressure degasser, by increasing the amount of NH-rich condensate and by lowering the temperature and raising thepressure. In most instances, the major portion of the off-gases, whichare mostly hydrogen and methane, are released in the high pressuredegasser. Usually about to volume percent of the dissolved gases flashoff in the high pressure degasser. Therefore, there is only a relativelysmall quantity of H 8 carried off with the off-gases from the lowpressure degasser. Thus, in accordance with the present invention,nearly all the H 8 is left in the aqueous phase so that it may berecovered as one overhead stream from the H 8 stripper.

The aqueous solution from the low pressure degasser is introduced tofeed surge tank 12 wherein a residence time preferably between 3 and 24hours is provided. The feed surge tank 12 should be a floating roof tankor inert gas blanketed. If air is allowed to come in contact with theaqueous solution, hydrogen sulfide will be oxiodized to form freesulfur.

Aqueous solution is withdrawn from the feed surge tank via line 13 andintroduced to H S stripper 14. Due to heat input in the bottom of the H8 stripper, hot upflowing vapors are generated which serve to strip H Sout of the aqueous solution. A cool stream of water is introduced vialine 16 to the upper part of the H 5 stripper so as to generate adownward flowing aqueous stream which serves to fractionate the NH fromthe H 8. A relatively pure stream of H 8 is withdrawn via line 15 fromthe top of the H 5 stripper. The NH content in this H 8 stream isusually less than 2 Weight percent, commonly as low as a few tenths of apercent; and preferably the H 8 stripper conditions are maintained so asto result in an N'H content of less than l00 p.p.m., for example, 10 to30 p.p.m.

An aqueous solution which is rich in NH but still containing substantialamounts of H 8 is withdrawn via line 17 from the bottom of the H 8stripper. This stream is fed to NH;; stripper 18. Hot upflowing vaporsare generated by heat input into the bottom of the NH;, stripper. Thesehot upflowing vapors serve to strip NH and H 8 out of the aqueoussolution fed to the NH stripper. A purified Water stream is withdrawnfrom the bottom of the NH stripper via line 19.

A vapor stream comprised of H 0, NH and H 8 is withdrawn from the top ofthe NH, stripper via line 20. The operating conditions in the NHstripper are controlled so as to regulate the amount of H 0 in the vaporstream in line 20 so that, when this vapor stream is partially condensedin condenser 21, the liquid condensate formed and withdrawn from thecondenser in line 22 will contain a very large fraction of the H 8present in the overhead system. Thus the NH withdrawn as a vapor in line24 is substantially freed of H S. The H 5 content in the NH vapor isgenerally less than about one to two percent and may be reduced to aslow as 0.1 to 0.5 percent H 8 by volume. The condensate which is formedby cooling the NH stripper overhead vapors in condenser 21 is rich in NHTypically, the ratio of =NI-I to 'H S will be between 10:1 and 2:1 inthe condensate withdrawn from reflux drum 23 via line 25. Preferably,the ratio of NH to H 3 is between 321 to 6:1 on a molar basis. A portionof this NH -rich condensate is refluxed to the NH; stripper via line 27to provide cool, downward flowing liquid in the upper part of the NHstripper. According to the process of the present invention, a secondportion of the NH -rich condensate is recycled via line 26 to becombined with the net feed introduced to the process via lines 1 and 2.

In the present invention it is preferred to control the amount of NH-rich condensate which is recycled, as well as the ratio of NH to H 5 inthe recycle, so that the ratio of NH to H S of the combined streams fedto the high pressure degasser is at least 1.1:1.0 on a molar basis. Forstreams which contain more than a percent or two of dissolved NH and H 8it is preferable to use more recycle NH -rich condensate, so that theratio of NH to H S (calculated as separate species) is at least 1.2 to1.0, and in many instances it is preferred to have as much as one andone-half to about five times as much NH as H28.

EXAMPLE This example illustrates the advantages obtained using theprocess of the present invention for treating aqueous streams whichcontain large amounts of H 8 relative to NH in addition to lighthydrocarbons and/or hydrogen dissolved in the aqueous stream due to highpressure.

A solution comprised of about 984 pounds of H 8, 516 pounds of NH andabout 760 standard cubic feet of hydrogen plus light hydrocarbonsdissolved in 27,820 pounds of H is obtained by water washing ahydrocracker reactor eflluent. The hydrocracker reactor eflluent streamwhich is water washed is at about 250 F. and 1,250 p.s.i.g. The aqueousstream thus obtained is introduced via line 1 to the processschematically illustrated by the drawing, except that there is norecycle NH -rich condensate to the high pressure degasser. Part of theNH rich overhead from the -NH stripper is, however, recycled I directlyto the H 8 stripper.

An aqueous solution comprised of 28,000 pounds of H 0, 436 pounds of H 3and only trace amounts of NH is obtained as overhead condensate from afractionating column in the fractionation section of the hydrocrackingunit. This stream is introduced via line 2 to the process. In this firstinstance, the NH -rich condensate from the overhead of the NH stripperis recycled directly to the H 5 stripper. The above streams and theresulting streams corresponding to the numbered streams shown in thedrawing are summarized in the table below:

TABLE I Stream No HgO,1b./h1. HgS, lb./l1r. N11 lb./hr.

The combined streams 5 and 10 contain about 760 s.c.f. of hydrogen pluslight hydrocarbons.

Using the process of the present invention, identical streams 1 and 2are fed to the process schematically illustrated in the drawing. Inaddition, a portion of the condensed overhead from the NH stripper 18 isrecycled via line 26 to the high pressure degasser. This recycle streamis rich in NH, relative to H 8. The moles NH in the recycle stream are26.2; the moles H S total 8.7, thus resulting in a molar ratio of NH toH 5 of about 3.01. There is suflicient NH in the NH recycle via line 26so that the re sulting combined streams in line 3 have a ratio of NH toH 8 on a molar basis greater than 1.0. Preferably, the ratio of NH to H5 in stream 3 is maintained above 1.1.

8 I In this example, the ratio of NH to H 5 is 1.22. The feed streamsand resulting streams are summarized below:

The combined streams 5 and 10 contain about 7 60 s.c.f. of hydrogen pluslight hydrocarbon gases.

As can be seen from the comparison of streams 5 and 10 in Table 'II tostreams 5 and 10 in Table I, the H 8 losses are drastically reduced.Using the process of the present invention, the H S losses are reducedfrom 400 pounds per hour (Table I) to 4 pounds per hour (Table II). Thusthe process of the present invention results in reducing the H S presentin the flashed 0ft gases by a factor of 100 in this example. Thusrecycling NH -rich overhead condensate from the NH stripper is ofparticular advantage when feeding streams which have relatively largeamounts of H 8 compared to NH When the H 5 concentrations in the netfeed streams are lower, the advantage is correspondingly reduced, butgenerally the H 8 loss is reduced by a factor of at least five. Also,the recycle of the NH -rich condensate will still serve to some degreeto help retain H S in the aqueous phase so that it may be recovered vialine 15 as a unitary product stream. Furthermore, the recycling of NH-rich condensate to the degassing section instead of directly to the H 5stripper has the very important advantage of improving control stabilityof the H 8 stripper and the NH stripper.

Although various specific embodiments of the invention have beendescribed and shown, it is to be understood they are meant to beillustrative only and not limiting. Certain features may be changedwithout departing from the spirit or essence of the invention. It isapparent that the invention has broad application to the recovery ofseparate streams of H 8 and NH from aqueous solutions of the same.Accordingly, the invention is not to be construed as limited to thespecific embodiments illustrated but only as defined in the followingclaims.

I claim:

1. A process for separately recovering an H S-rich stream and an NH-rich stream from a first aqueous solution comprising H O, H S, NH anddissolved methane under superatmospheric pressure according to thesteps:

(a) combining at least a portion of an NH -rich overhead condensate withthe first aqueous solution to obtain a combined aqueous solution havinga molar ratio of NH to H 8 of at least 1.1 moles NH to 1.0 moles H 8;

(b) removing from the combined aqueous solution at least volume percentof the dissolved methane as a gas by reducing the pressure on thecombined aqueous solution to a pressure at least below 200 p.s.i.g. tothereby flash off methane;

(c) providing at least one hour residence time for the combined aqueoussolution; and then (d) passing the combined aqueous solution to a firstdistillation column;

(e) stripping H 5 out of the second aqueous solution in the firstdistillation column to obtain an H S-rich overhead stream and an aqueousbottoms stream of reduced H S content;

(f) stripping NH out of the aqueous bottoms stream of reduced H Scontent in a second distillation column to obtain an NH -rich vaporoverhead; and

(g) partially condensing the NH -rich vapor overhead to obtain an NH-rich vapor stream and said NH rich overhead condensate.

2. A process according to claim 1, wherein between about 3 and 24 hoursresidence time is provided for the combined aqueous solution beforepassing the combined aqueous solution to the first distillation column.

3. A process according to claim 1, wherein at least 24 hours ofresidence time is provided for the combined aqueous solution beforepassing the combined aqueous solution to the first distillation column.

4. A process according to claim 1, wherein the combined aqueous solutionis degassed first in a high pressure degasser at a pressure between 50and 500 p.s.i.g. and then is degassed in a low pressure degasser at apressure between and 50 p.s.i.g.

5. A process according to claim 4, wherein the combined aqueous solutionis degassed first in a high pressure degasser at a pressure of between70 and 200 p.s.i.g. and then is degassed in a low pressure degasser at apressure between 1 and 10 p.s.i.g.

'6. A process according to claim 4, wherein the gross feed to the highpressure degasser is comprised of:

(a) an aqueous solution of H 5, NH light hydrocarbons, and hydrogen(stream a) obtained by contacing with water the eifiuent from ahydroconversion proces at a pressure of at least 500 p'.s.i.g.,

(b) an aqueous solution comprised of H 5 and light hydrocarbons (streamb), wherein the H S content is such that the combined streams (a) and(b) have an NH to H S molar ratio less than 1.1210, and (c) the NH -richcondensate stream (stream c) from the overhead of the NH stripper, andwherein the amound of NH in the NH -rich condensate recycled from theoverhead of the NH;,, stripper is sufiicient so that the combinedstreams (a), (b) and (c) have an NH to H 8 molar ratio of at least1.1:1.0.

References Cited UNITED STATES PATENTS WILBUR L. BASCOMB, 111., PrimaryExaminer US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,518,166 June 30, 1970 Robert J. Klett It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, lines 5 thru 9 should be deleted and the following insertedinstead therefor action effluent, a portion of these light hydrocarbons,as well as a small portion of the hydrogen, will dissolve in the waterphase, particularly if the washing is at a high pressure. In manyhydroconversion processes, the washing is done at a pressure of 500 to5,000 psig, more Signed and sealed this 20th day of October 1970.

'(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

1 Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents

